Hello I'd like to buy a TI-84 + CE of some sort but I would like it to be the one that wasn't jailed.
I'm not opposed to buying used. Is there a way to tell by the barn on date or something if the calculator still allows Assembly language programming?

Or do the new jailbreak methods work well enough so this really isn't a concern?

ArTIfiCE works on all CE's, which lets you run ASM programs. On CE's with revisions pre-M, which is the letter (or two) after the date code, there is another exploit that does something more powerful, but you get that at the cost of a slower calculator.

You have to get a calculator where TI-OS is in a version BEFORE 5.5. However, arTIfiCE is still effective, and in combination with ASMHOOK, (running) assembly program functionality is restored.

Getting an OS 5.5.1 or later is still okay with those exploits. If it is before 5.5.1, no exploits are required. Otherwise, you need arTIfiCE.

Obviously since they can be updated, there's no way of knowing for sure when buying used.
That being said, if you're willing to gamble on it not being updated, you should look for the RCM triangle before the dustbin symbol on the back, and the fractions silkscreening to be missing on the front.
If it has both of those things, that places it in the sweet spot (pre-O and post-M), so it would have shipped with either 5.3.6 or 5.4.0.

Clever tells!
So look for the missing fractions.

What's the drawback to a pre 5.3.6?

5.3.6 is just what rev Ms shipped with. M+ hardware is desirable because it's generally much faster than earlier revisions.