Right, if they are "normal" spawners (i.e. the type that you would find out in the world), then that collection would be easy to get. Skeleton and Zombie spawners are common in the TC3 barrows, blaze spawners are relatively easy to get ahold of. The would just need to be moved by portal gun/gravity gun (which are common finds in dungeons). Pig spawners are available from a bug with portal gun, whereby if a spawner is "dropped" onto a torch, the block drops, but reverts back to the standard pig spawner.
Given the distribution that you've explained, this is the most likely explanation.
If they are soul-shards spawners (i.e. ones crafted by killing mobs to charge up with their souls), it is still possible by exploiting the above bug to gt a large number of pig spawners, and use those to charge the shards. These can be combined in an anvil with a "typed" shard to get a high-level shard of certain types (i.e. blaze, ghast, etc.).
The top explanation is more likely to my mind, because the spawners mentioned are all of types that are relatively accessible in world (zombie, skeleton, pig, blaze), but either way I would not be concerned about a collection like that after 3 weeks.