if you are like anyone, even having played for 5 years, you might have lots of gear but be missing lots of recipes. and from the wording of your question i see you are confusing recipes with gear.
just look at your own craft screen and count the number of lower right missing dots (i will not name color as i am color blind).
or use the fan site info. here is mine, and if i bought that item guess what recipe i might get? one for Sal who has had LLL gear for 5 years but is missing recipes.

You own 133 on 137 available crusaders and have on them these gears: common = 0 - uncommon = 0 - rare = 2 - epic = 70 - golden epic = 8 - legendaries = 304 - golden legendaries = 15 - total levels of legendaries = 642 - Legendaries calculated in power as level of materials spent to reach that level (L1=0, L2=1, L3=3, L4=7, L5=15, L6=31...) = 2182
Recipe owned: 396 common/uncommon (99%), 396 rare (99%), 327 epic (82%), total 1515 (95%) - Graham the Driver, James the Seated and Kathleen the Chaotic excluded from statistics

p.s. i have not updated that to include this events new guy and perhaps some missions results. but you see there are a whole lot of epic recipes that 1495 day old me does not have.

i do not know which they decide. it might be that they go totally random or that they go for most recent, or they go for the most useless ( would be shameless but i can see some companies doing that).
all such 'decision' points are a very simple thing to program and only the devs if they choose to answer this good question can say what theirs is.