I've had the same experience with some exponents assigned to me. My guess is that someone has been doing trial factoring work semi-independent of PrimeNet and has just reported all the work that they have done.
This is probably a good explanation - especially in light of your point #2
1. For a long time on this page: http://mersenne.org/primenet/ there where no exponents in the range listed 21.9M to 22.0M. This has recently changed with them now all being listed as available for first time Lucas Lemer testing.
These exponents were manually reserved a year and a half ago for some trial factoring work. Yesterday, I cancelled that reservation and added the exponents to the server.
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