SN 6.13 ratio of sekhas to arahants

Just my notes, no conclusion, just wondering.

Thanissaro translation: 

In a single holy life,
a thousand have left death behind.
More in training,
five hundred plus
ten times tenfold ten:
All have attained the stream
that never leads to an animal birth.

500 + 1000 = 1500 trainees

(all = 1000 + 1500) 2500 stream enterers

Bodhi's translation, I thought it might be saying

1000 arahants,

1500 sekhas ( 500 more nonreturners and once returners than arahants)

10x10x10 x (1000 + 1500) = 2500 x 1000 stream enterers

Obviously verse is tricky to say with any certainty,

1) wondering if sekha here in SN 6.13 (or in general) tends to refer to non-returners and once returners (excluding stream enterers)

2) wondering if this sutta is meant to give a breakdown of ratios between various types of enlightened beings, like in 

SN 8.7

“Imesampi khvāhaṃ, sāriputta, pañcannaṃ bhikkhusatānaṃ na kiñci garahāmi kāyikaṃ vā vācasikaṃ vā.
“There is nothing, Sāriputta, that these five hundred monks have done by way of body or speech that I would criticize.
Imesañhi, sāriputta, pañcannaṃ bhikkhusatānaṃ saṭṭhi bhikkhū tevijjā, saṭṭhi bhikkhū chaḷabhiññā, saṭṭhi bhikkhū ubhatobhāgavimuttā, atha itare paññāvimuttā”ti.
For of these five hundred monks, sixty have the three knowledges, sixty have the six direct knowledges, sixty are freed both ways, and the rest are freed by wisdom.”

I interpret the meaning of that passage, using ratios of each group,  to give the reader a rough idea on the relative difficulty of having only 3 of the 6 higher knowledges, having all 6, having formless attainments, and only 4 jhanas.

I was thinking SN 6.13 might be doing something similar with arahants and sekhas.

B. Bodhi's translation SN 6.13

 601 “For this has actually been seen by me,

It is not merely hearsay:

Within a single holy life

A thousand have left Death behind.
416

602 “There are five hundred more trainees,

And ten times a tenfold ten:

All have entered the stream,

Never returning to the animal realm.

603 “As for the other people who remain—<335>

Who, to my mind, partake of merit—

I cannot even number them

From dread of speaking falsely.”  

(pali + english trans. based on sujato)

SN 6.13 Andhakavinda: At Andhakavinda

13. Andhakavindasutta	13. At Andhakavinda
Ekaṃ samayaṃ bhagavā māgadhesu viharati andhakavinde.	At one time the Buddha was staying in the land of the Magadhans at Andhakavinda.
Tena kho pana samayena bhagavā rattandhakāratimisāyaṃ abbhokāse nisinno hoti, devo ca ekamekaṃ phusāyati.	Now at that time the Buddha was meditating in the open during the dark of night, while a gentle rain drizzled down.
Atha kho brahmā sahampati abhikkantāya rattiyā abhikkantavaṇṇo kevalakappaṃ andhakavindaṃ obhāsetvā yena bhagavā tenupasaṅkami; upasaṅkamitvā bhagavantaṃ abhivādetvā ekamantaṃ aṭṭhāsi.	Then, late at night, the beautiful Brahmā Sahampati, lighting up the entirety of Andhakavinda, went up to the Buddha, bowed, stood to one side,
Ekamantaṃ ṭhito kho brahmā sahampati bhagavato santike imā gāthāyo abhāsi:	and recited these verses in the Buddha’s presence:
“Sevetha pantāni senāsanāni,	“One should frequent secluded lodgings,
Careyya saṃyojanavippamokkhā;	and practice to be released from fetters.
Sace ratiṃ nādhigaccheyya tattha,	If you don’t find enjoyment there,
Saṃghe vase rakkhitatto satīmā.	live in the Saṅgha, guarded and rememberful.
Kulākulaṃ piṇḍikāya caranto,	Walking for alms from family to family,
Indriyagutto nipako satimā;	with senses guarded, self-disciplined and rememberful.
Sevetha pantāni senāsanāni,	One should frequent secluded lodgings,
Bhayā pamutto abhaye vimutto.	free of fear, freed in the fearless.
Yattha bheravā sarīsapā,	Where dreadful serpents slither,
Vijju sañcarati thanayati devo;	where the lightning flashes and the sky thunders
Andhakāratimisāya rattiyā,	in the dark of the night;
Nisīdi tattha bhikkhu vigatalomahaṃso.	there meditates a monk, free of goosebumps.
Idañhi jātu me diṭṭhaṃ,	For this has in fact been seen by me,
nayidaṃ itihītihaṃ;	it isn’t just what the testament says.
Ekasmiṃ brahmacariyasmiṃ,	Within a single spiritual dispensation
sahassaṃ maccuhāyinaṃ.	a thousand are destroyers of Death.
Bhiyyo pañcasatā sekkhā,	And of trainees there are more than five hundred,
dasā ca dasadhā dasa;	and ten times ten tens;
Sabbe sotasamāpannā,	all are stream-enterers,
atiracchānagāmino.	freed from rebirth in the animal realm.
Athāyaṃ itarā pajā,	And as for other people
puññabhāgāti me mano;	who I think have shared in merit—
Saṅkhātuṃ nopi sakkomi,	I couldn’t even number them,
musāvādassa ottapan”ti.	for fear of speaking falsely.”

B.Bodhi's footnotes:

416 Spk explains itihītam in pāda b as if it meant deduced by reasoning or logic or inferred from scripture (idam itiha itihā ti na takkahetu vā nayahetu vā piṭakasampadānena vā aham vadāmi).
The use of the expression elsewhere, however, indicates that it is specifically connected with oral tradition, e.
g., at MN I 520,4:
so anussavena itihītihaparamparāya piṭakasampadāya dhammam deseti;
“he teaches a doctrine by oral tradition, by transmission of hearsay, by what has come down in scriptures.”
See too MN II 169,12.In pāda d, the thousand who have left Death behind (sahassam maccuhāyinam) are the arahants.

417 I interpret the numbers in v.602 with the aid of Spk, even though this leads to the unlikely conclusion that the number of stream-enterers is not significantly higher than the number of arahants (cp.55:5, V 406,11-30). 

I read pāda b with Be, Se, and Ee2 as dasā ca dasadhā dasa rather than with Ee1 dasā ca dasadhā satam.
Though the latter gives a ten times higher figure, it does not agree with the commentary, which glosses:
dasadhā dasā ti satam.
It is not clear to me whether the “five hundred more trainees” (bhiyyo pañcasatā sekkhā) means that there are fifteen hundred trainees between the arahant and stream-enterer stages plus an additional thousand stream-enterers, or fifteen hundred trainees who are stream-enterers.
V. 603 is also at DN II 218,6-9, uttered by Brahmā Sanaṅkumāra after he has said that twenty-four hundred thousand (not twenty-four hundred, as Walshe has it at LDB, p.299) Magadhan followers had passed away as stream-enterers and oncereturners.
According to Spk-pṭ, “the other people who partake of merit” (itarā pajā puññabhāgā) are those who have partaken of merit aimed at the ending of the round (but who, presumably, have not yet reached any path or fruit).