Hmm. Just tried another store and same issue. My GC Splinter Cell did NOT get the automatic $5 bonus. I didn't want to fight it, so just went ahead and traded it in. Maybe it's only that specific game? Also can confirm the $30 TIV for the switch games. got $38 for them with the pro bonus.
EDIT...
yeah GC version. I'll report back after I try a different store tomorrow. The person who rang me up today did put some sort of retro refurb fee for $0.00 though. Maybe that's why, we'll see.
Tried trading in Splinter Cell: double agent today at my local store. Didn't automatically get the $5 bump, so I held onto it. Retro games may not work anymore. The X360 and PS3 games worked fine though. Going to try another store tomorrow and see if they'll manually add on the $5 for me. Good...