You use whatever terminology you're comfortable with Tom. I'm certainly not out to bash people for it in casual conversation. At the same time, it is very useful to have everyone on the same page when it comes to specific arsenal stamps. It makes no sense for the admin running this board to dictate 'this stamp is XYZ' when there is no evidence to corroborate it and there are questions and outright disagreements regarding what the characters say or how they are ordered. If there is hard data (like for the /256\'s), then we can call it and feel comfortable that there is a valid reason for that decision. /?5\ /0306\ or /0406\ is your call. It may get tiring hearing people ask for photos to understand what it is you're designating a /0306\ though.
You have a great looking carbine there. It fits well with the month-year scheme as well. As for preban vs post, do you live in a state where it actually matters? Federally, that designator died with the sunset of the AWB and makes no difference anymore. I always assumed that those that were concerned with the pre/post designator at the state level required documented proof (orig sales receipt with legible date, etc.) otherwise the gun was assumed to be post.