you were blowing out the team and it went to garbage time, where the coach always takes the starters out for some rest and the bench in for minutes. it's how a typical blowout is supposed to be.
Except that the coach, given free reign, didn't and doesn't do that. The coach "always takes the starters out", except when using LCD. Also, this is a regular occurrence with LCD - I constantly see my starters play regular minutes under LCD, even in blowouts. Either this is a "feature, not a bug", or LCD is faulty.
Are you certain in those other games that "garbage time" was truly triggered? Open the play by play, and search for garbage time. In you last game, garbage time was called with <1 min to go in the 3rd quarter. When this happens, the coach will try and remove all starters from the game (regardless of whether it's LCD or SFDC - I think the main exception is LCD with a blanked lineup).
In these cases, in order to maximize the chances that your player of interest (typically a trainee) doesn't get removed at garbage time, you have to limit the number of players on the bench. In that case, usually the backups at the other positions will get subbed into the game, leaving your trainee still in the game. This is why people suggest to field only 9 players in the lineup when trying to get a guy 48 minutes. If you've gotten it to work with LCD in the past, it may be that your starter was much better than the guys on the bench.
I conceptualize it as follows:
Everytime there's an opportunity to make a substitution, the coach looks at his starters and the possible guys on the bench. Then, he makes a judgement about their relative abilities, as affected by their stamina and minutes played thus far. He looks at every player on the bench, but weighs them by their position on depth chart. If the option on the bench is better than the guy on the floor, he'll make a change. So, a guy off the depth chart can be inserted, but his ability must be much much better than the alternative for it to happen. Also, when garbage time is called, these rules change a bit, and the coach may make more changes, when the result is taking out the starter.
When the sub pattern is set to LCD, I think the coach just goes with whoever is best. With SFDC, I suspect the switch is usually made when the starter gets to a certain level of reduced ability, due to stamina.
These rules lead to some odd happenings.
All cases, relatively crappy backups won't play as much (since even the stamina decreased starter is still better).
In SFDC, high stamina guys with better skills than their backup may play the entire game.
In SFDC and garbage time, the player in all three spots of the depth chart (starter, backup, reserve) can get subbed out in the last few minutes if a starter on the bench is much better (say you're training a guard at PG, and the SG starter is really good, much better than your trainee. When garbage time is called, the starter SG goes to the bench. He sits there until the end of the game, as the trainee PG gets worse, and the SG improves from rest. At some point, even with SFDC, the coach may insert the SG into the PG position).
As far as SFDC, you should fill in all the depth chart gaps, and definitely the starters. You won't forfeit, as long as there are guys in the active lineup, but the coach chooses total crazy players at bad positions, e.g. centers at PG. hrudey once suggested that bot teams use SFDC with blank lineup, and after accidentally using that in some PL games, I agree.