I think Tandy is full of BS. Methinks they just want to move their Eco-Flo subpar brand over anything else and are willing to self-sabotage some of the merchandise they carry in order to do so: case in point: Fiebing's. As long as it's ground-transported, any carrier can deliver Fiebing's "combustible" Pro dyes. Hare-brained shenanigans from Tandy.
I'd NOT stitch before dyeing: you'll dye the thread!
Thus, I'd dye, then wet mould, then stitch. Stitching would always be my last step—well, technically, the last step would be the edge finishing, but you get my drift.