Creating multirow panorama in LR6

LR has 2 limits (kicking in with what happens first): 65k height or width (or both) or 512 megapixels. if you shoot a pano you may roughly precalculate from the source files to get an estimation about reaching this limits. given a usual overlap of a 3rd take 66% of the source files edge leading in the direction of assembly, so usually the short edge as most panos are captured in portrait mode. respectively, an overlap of 1/4 (easier for a quick calculation) results in 75% usable width of every photo, so with a 24MP cam you have 4000x6000 pixels, and with 25% overlap, you can use 3000 for the pano. divide 65k by 3000 you get about 22 images width for reaching the width limit. assuming a 2 row pano of this width, you have 24MP x 0.75 x 0.75 x 44 you get a 594 MP result which overrules the 65k limit.
(btw, CR has similar limitations, while PS can stitch larger images. in PS, mostly you run into memory issues with very large stitchings.)