It’s not unusual to see Patek Philippe watches at auction, but two examples in the Sotheby’s Important Watches sale in New York last December stood apart.

The watch dials had been altered especially for the consignor, a longtime Patek Philippe customer who wanted them to be more readable because of his failing eyesight. The adjustments were subtle: repainted hands on one model and greater dial/hand contrast on the other. But since any customized Patek Philippe is exceptional, it was enough to call them unique pieces — and to warrant a premium price.

“This is really rarefied air,” said Geoff Hess, Sotheby’s global head of watches. “If an owner is prominent enough, and has done enough with the brand, Patek might make something unique for them, but you almost never see them.”

Of the two watches sold in December, one — a Ref. 5070P-001 chronograph — would normally sell in the $175,000 range, but “went for $482,600 because of the customization,” Mr. Hess said. The other watch, a Ref. 5970G-001 perpetual calendar chronograph that originally retailed for $89,600 and trades on the secondary market in the $300,000 range, sold for $508,000. Both watches have been out of production for many years.