Notes on Summoning

It is a little known and oft-overlooked detail that most summoning spells capable of conjuring allies to the battlefield, such as conjure animals, conjure woodland beings, conjure fey, and conjure celestial, do not permit the player to choose the exact creature(s) summoned by the spell. As specified by these spells, the player indicates the desired CR they wish to summon, at which point the game master chooses creatures appropriate to the scenario, environment, or request.
There is no guarantee spells capable of summoning multiple creatures, such as the conjure animals spell, will summon identical creatures for each slot. If you ask the game master for eight CR ¼ beasts, you might get an assortment of creatures who answer your call.