It may be obvious but are you sure that you are looking at R value when you were checking those transactions and their signatures? You see signatures are encoded using DER encoding and there are certain bytes added in that which are always the same (eg. 4730440220 which is [stack size][sequence tag][sequence length][int tag][int length]).
k=689633
65C5 0007A87 B2954B63C8658A956B756DCF7CEC554445EEF1D18CECD6E79262
p00yA87
Actually something comes to my mind.
I wonder if someone deliberately prepared the k's in advance and created the tx's themselves.
He didn't take the trouble and spread it over 2 years, and also made 1000 btc volume in the wallet time. He may be a patient and humorous person.