Drop-in resolution
Miyota 8245 vs Seiko NH70 (TMI NH70A): do they swap?
Whether the Miyota 8245 and Seiko NH70 (TMI NH70A) share a case, and what changes if you move between them.
Different footprints. The Miyota 8245 is 26.00 mm x 5.67 mm and the Seiko NH70 (TMI NH70A) is 27.40 mm x 5.32 mm, so they do not share a case. This is a choice between platforms, not a swap.
The Miyota 8245 is the fullest-calendar 8200 member, with day, date and a 24-hour indicator. The Seiko NH70 (TMI NH70A) is the fully skeletonised member of the NH3x family, in open-worked mod watches.
They differ in diameter (26.00 mm vs 27.40 mm), height (5.67 mm vs 5.32 mm), calendar layout (centre seconds, day and date at 3, 24h sub-hand vs full skeleton, no date, no seconds hand), winding behaviour. An 8200-family caliber at 26.00 mm x 5.67 mm carrying day, date and a 24-hour sub-hand. It shares the family footprint with the 8205 and 8215 but needs a dial printed for its added complications.
Matching diameter and height is necessary but not sufficient. A donor is only a true drop-in when the dial-foot positions, hand-hole sizes, stem length and calendar layout also match. Two movements can share a case and still need a new dial, re-broached hands or a cut-to-length stem.