The missions pretty much just say, pick me an available ship in the BPV range X-Y.
For 2271, if you take a look at the BPV range 113-133 (which covers a pretty good chunk of the common drawing bpv), you'll find the available klingon ships are:
Drone boats: D6D, D6DB
Maulers: MD5, D6MK
Carrier: D5VK
Escort: D5E
Other: D6K, D5L
That means that if you grab three ships in that bpv range there's about at 58% chance at least one is a mauler.
(And only a 1/64 chance that you won't be facing at least one specialty ship).
<shrugs> Unfortunately, BPV ranges are the only things the scripts can use to avoid out-of-era drafting, so as long as there is an abundance of draftable specialty ships in the list in any given year(s), that's what we wind up fighting.
(Similarly, in the Rom list in the 113-137 bpv range in 2271, 2 of the 5 ship available for drafting are maulers.)
One suggestion that might work is to create a variety of restricted line ships, e.g. the D6K1, D6K2, etc, with the same stats. That way they won't clutter the shipyards but will be more common as AI opposition, and the "desirable" specialty ships can be kept in the list and shipyards.
We'd only want to do that with a handful of line ships from each race, preferably ones with long lifespans in the shiplist (to prevent bloating the shiplist too much), but it is a possibility.
dave