Or it means that the drive has failed one bad flash page (4KB) and relocated it and is reporting how many 512 byte sectors it moved when it did that.
Just to clarify, my assumption that all the spares were exhausted stems from the OP's description how a single logical address is appearing in the Event Log. Re-reading his post I see that he doesn't specifically say it's the same address every time.
If it's the same address, then the spares may very well be exhausted. If there would be spares available, that logical address would be reallocated to a different (working) physical address and it would no longer get reported.
Even if it's not the same address every time, if a large part of a flash chip is faulty, you'd get errors on many logical addresses, since none of them can reallocate anymore.
I agree with the hypothesis that the reallocation is failing because the drive had already exhausted its entire supply of 8192 spares.
Hey, somebody agreeing with me! Wish my wife did that from time to time.
What I'm curious about is how many reallocations do I get on my 128 gig M4. I'm on AD = 180 (6% of lifetime), with zero (01) and (05). Hope it stays that way for the next 31 years that I'll need to get to 100%.