It's worth understanding how stat changes work in MM1 and MM2. (I've only played MM2, but from what I've read on this forum, MM1 works more or less the same way.)

Every stat actually has two values: the base value and the current value. (Exceptions are current HP and (at least in MM2) current and maximum SP.) Most of the time, the values are the same, but some events can change one or the other. MM2 has fountains that change the current values of your stats, for example. There are also spots that increase your base stats, but *they do not increase your current stats*. (For example, you might have your base speed increased from 14 to 24, but your current speed remains the same for now.)

The other important rule to understand: after every battle, your current stats are set to your base stats. (Exception: in MM2, this doesn't happen to Maximum HP.) (Another exception: in MM2, a character who runs individually from battle will not have her stats reset. This can be used to make the Heroism spell not wear off when the battle ends.) Your stats also return to their base values when you rest (this includes Maximum HP) and, in MM2 (another posts suggests not MM1 here), when you get healed at the temple. (Exception: If you rest while poisoned your current Max HP is set to *half* of the base. As far as I know, this is all poison does.)

As a result of this, you can get an increase (or decrease! happens in one spot in MM2) to one of your base stats and not notice it right away.

If any of this works differently in MM1, please tell me in a reply to this post.

I didn't get that impression when I played, but I agree that it could seem ambiguous. What was more confusing to me was what "worthy" meant. Eventually I figured out that all my characters had started the game worthy, which let them increase their stats once. But to become worthy again (and therefore increase their stats again), they had to do some specific tasks. There are hints to what those are among the statues in Sorpigal, if I recall correctly.

I assumed the worthy stuff just wasn't fully baked. Like it intended to be "become worthy and then come back here", but then it was changed along the way during playtesting without fixing the messages. Or something along those lines.