Sometimes it's important on SF to remind people that generalized preferences--especially those that serve as differentiators between people here and the general population--are still just preferences. The "detail policing" on here can get ridiculous, to the point of spectators telling people that their jackets are obviously orphans simply because they have flap pockets when the jackets were produced MTM or MTO.
Patch vs. flap is a preference. It can be informed by stylistic tradition (e.g. Neapolitan vs. Savile Row vs. northern Italy), but it's not a signifier of inherent wrongness. Greg Lellouche will happily sell you a flap pocket SC or a patch pocket suit. We seem to think he knows what he's doing, so perhaps that's an indicator?
I would say that if you are going to get an odd jacket MTO or MTM, you want to be conscious of not having it look like an orphaned suit jacket if you can help it. Texture of the fabric, patch pockets and different buttons than you'd typically see on a suit jacket all help with this. I agree that if we start saying anything with flap pockets is an orphan it gets to be a bit absurd, but I think in general the focus on detail is helpful and is precisely what one should expect and want out of a hobbyist forum. I agree that patch vs. flapped is a point of preference vs. a rule, but some jackets would really benefit from some casualizing features to avoid looking like orphans.
FWIW, my DB navy blazer has flapped pockets and metal buttons. My F/W SB one has two patch and metal buttons. My S/S SB one is a RAF blue linen with 3 patch and smoked MOP buttons.