The personal/frontpage distinct came much later than when those posts were written, we must have set the default on old posts to be personal, and I guess no one went back and frontpaged all the ones that were.
There are an enormous number of posts that predate this distinction, and retrospectively categorizing them seems like a lot of work for minimal benefit, so this seems fine?
Many (most?) posts in the Sequences are tagged as [Personal Blog] instead of [Frontpage]; is this deliberate?
Here are a few examples from posts that I recently had reason to consult:
Belief in Intelligence:
Aiming at the Target:
Measuring Optimization Power:
Efficient Cross-Domain Optimization:
(There are several others, these are just the posts I had reason to interact with today).
Perhaps they should be moved to the front page? Several posts there seem obviously fitting for front page material, and they are quite central to the LW community.