Unusual Wordforms

I was perusing through a variety of texts this morning looking to see whether all of the wordforms I’m using in my morphological analysis/database are attested in the texts that I have on my computer: Josephus, Philo, LXX, NT, Apostolic Fathers, and the Pseudepigrapha.

Thus far, I’ve found all of my wordforms.

But in the process, I’ve come across some unusual forms that I really don’t know what to do with – all from the Greek Pseudepigrapha:

ἀγαθοῖσιν and ἀγαθοῖο

I’m guessing that its dialectal difference, but I know too little about Greek dialects to say for sure and I’d be curious if anyone has any suggestion. The first form is quite obviously a Dative Plural, either masculine or neuter (in this case its masculine, modifying ἀνδράσι; Sibylline Oracles 5.69).

As for the second, form, it appears to be a genitive since it follows a genitive preposition (ἀντ’ – Sibylline Oracles 1.46).

If anyone has any comments on these forms themselves and their origins, I’d be interested. There are numerous examples of “normal” genitive and dative forms throughout the texts.