In previous zabbix versions (pre 2.1.x) Latest data's Last check value was displaying checks facts timestamp. It didn't matter whether check result was successful or unsupported - the timestamp was updated either way, and glancing at Last check user could easily figure out when the last check actually occured.

Due to the changes introduced in ZBXNEXT-1689, Last check now displays a timestamp of last received value. Unsupported check timestamps are not registered in the db anymore.

Therefore "Last check" does not correctly describe the data it is displaying now. It should be renamed to "Last successful check", "Last value check", "Last value timestamp" or to something along these lines.