Drop-in resolution
Seiko NH36 (TMI NH36A) vs Miyota 8217: do they swap?
Whether the Seiko NH36 (TMI NH36A) and Miyota 8217 share a case, and what changes if you move between them.
Different footprints. The Seiko NH36 (TMI NH36A) is 27.40 mm x 5.32 mm and the Miyota 8217 is 26.00 mm x 5.67 mm, so they do not share a case. This is a choice between platforms, not a swap.
The Seiko NH36 (TMI NH36A) is the day-date sibling of the NH35, adding a weekday disc on the same footprint. The Miyota 8217 is the 8200-family member adding a 24-hour indicator alongside the date.
They differ in diameter (27.40 mm vs 26.00 mm), height (5.32 mm vs 5.67 mm), calendar layout (centre seconds, day and date at 3 vs centre seconds, date at 3, 24h sub-hand), winding behaviour. Shares the NH35's 27.40 mm x 5.32 mm footprint and stem, so it drops into an NH35 case. The only change is the added day disc, which needs a dial with a day window and correct printing. It is the unbranded 4R36.
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.