Mining drone - elite, Mining drone- improved, Mining drone - standard, Mining drone - advanced
These were dropped in low numbers from the npc high sec transport convoys until 2003 or 2004(?).
The Mining drone - advanced became the T2 Mining drone, so should not exist in game anymore (according to Entity).
Some (or all?) "Mining drone - Improved" were seeded (or renamed?) as "Mining drone - improved UNUSED" around 2005-2006, but that naming error was reversed by CCP in 2012.
They are now very rare, valued at upwards of 1 bn isk. In 2012, the mining drones were among a number of relic items that were accidentally deleted from the game, but were later restored.