The other major trope in this type of working relationship, which they usually save for the point beyond which the audience is frustrated with the amount of crap the undercover is tolerating from the handler and ready to rationalize him turning on the cop, is that he's actually a sympathetic character at heart. The reason he's such a hardass is because of the pressure he's under, either because he's doing the operation by himself, against the orders of this own bosses, for good reasons and pure motives, or else his own bosses are unreasonable and demand too much of the operation, and when the hero isn't around, the handler is arguing against the latest risk the bosses want him to take and tries to keep him from getting burned or sacrificed for some political goal.

Well, they do acknowledge that his sentence was shortened, and that it "checks out", plus he has his brother vouching for him. I imagine that Jax & Opie had a pretty smooth ride through the vetting process for SAMCRO. There is also the added credibility from killing the cop. That's a thing among the criminal community, and as you say, it's very unlikely that they would actually use or trust such a convict for undercover stuff.

Yeah, that's a good point.

OTOH, SoA wasn't all that tight with kids' ages. Abel grew a LOT, considering he was still an infant at the end of the first three seasons, and is a sentient toddler who can take direction at the beginning of the fourth, as the gang gets out after serving their 14 months. And by the last season, he's talking and comprehends Gemma's soliloquies enough to understand what she was talking about, to act out because of it and make Jax understand what he overheard. The final dissolution of the Teller-Morrow family comes about because Abel has sufficient communication skills to grasp and consciously reveal its ultimate secret. And IIRC, Thomas (conceived while Abel was an infant) is still a baby, so Abel can't be more than two.