The "lastshare" figure is not the difficulty of a miner's best share. It's the timestamp (in Unix time) of the miner's last accepted share.
The difficulty of a miner's best share in the current round is the "bestshare" figure.
The difficulty of a miner's all-time best share is the "bestever" figure.
The difficulty of a miner's best share in the current round is the "bestshare" figure.
The difficulty of a miner's all-time best share is the "bestever" figure.
thanks for the clarification