bridgedb should make clearer in its logs which addresses it knows are from bulk-exitlist

When I start bridgedb with loglevel INFO, it says things like

Dec 24 19:58:54 [INFO]   by location set: 59 50 56 50
Dec 24 19:58:54 [INFO]   by category set: 40

and then when I hit if from an IP in the 'category set', it says

Dec 24 19:59:17 [INFO] area is 87.236.194
Dec 24 19:59:17 [INFO] ---------------------------------
Dec 24 19:59:17 [INFO] category<1970>87.236.194
Dec 24 19:59:17 [INFO] Replying to web request from 87.236.194.158.  Parameters were {}

So I assume that means the category set is the same as the set of bridges it gives out when an IP from the bulk-exitlist file asks.

But the assignments.log gives no hint about which bridges are in this category set. Is it a subset of each ring? Or some other set that never gets logged in the assignments list? Confusing.