For me, having 4 core blends would be very hard to choose.
I need some burley as a core, between OJK and HH Burley Flake, I can't decide which would be in my core.
One VA based blend I suppose I would at this point pick Savinelli Brunello flake.
I also need an English in my core and I could make GLP Quiet Nights one of my core blends.
And finally my fourth blend as a core blend might be Mac Baren Navy Flake at the moment.
But it's a tough call. I don't think I could stay limited to that, but OJK or HH Burley Flake or both would always been in my core have to have, and some kind of English. But there's a lot I haven't tried yet, but of the many that I have, OJK and HH Burley are the only ones I could really point to and say "no question, this always has to be available to me, and I doubt any similar blend would supplant them as 'necessary'."