The longest continuously running line of complicated Patek Philippe watches, the perpetual calendar chronograph with moonphases is a cornerstone of the company’s production, with all its representatives being extremely collectible and some of them considered the ultimate tier of Patek Philippe production.

Most collectors can easily describe the general aesthetics of the line: three counters at 3, 6 and 9 o’clock, moonphases at 6, two windows at 12, and a round case - traits which are shared among all the five references which encompass the series: 1518, 2499, 3970, 5970 and 5270.

And yet, the aforementioned reasoning is if not wrong at the very least incomplete: it fails to take into account reference 5020, the sixth representative of the line and the one and only NOT sporting a round case, but rather a cushion one. A most unusual design choice, it is reminiscent of the 1920s production of the firm and was not very well received at the time, resulting in the most scarce output among the four modern references (3970, 5970, 5270 and indeed 5020): about 750 examples were made in all metals from 1994 to 2002.

Once again, however, the above classification is somewhat lacking, as it fails to take into account the gem-set variation of the models. Undoubtedly a superior tier of rarity, these opulent executions are extremely scarce most likely because their price combined with the fact that gem-set pieces were not as fashionable just a couple decades ago as they are now. These models usually bear a case number which differs from their standard counterpart by the digit “1” at the end the reference: ref. 5270 becomes 5271, 5970 becomes 5971, and indeed 5020 becomes the present astounding timepiece: ref. 5021.

While reference 5020 is undoubtedly elusive, reference 5021 goes well beyond what can be considered a simply “scarce” and well exemplifies how difficult it is to come across these 1990s gem-set models. So far, the auction market has seen only 4 examples of the reference: two versions in platinum, one in pink gold, and the present yellow gold piece - making this example, in fact, the only yellow gold 5021 to ever be publicly sold.

Intriguingly, the present watch bears luminous hands a characteristic which is not present on all the four known examples. This leads to the speculation that, given the importance of the purchase, Patek Philippe allowed the client to choose this detail according to their own desire.

The watch, offered complete of its accessories, was sold in 1996 and subsequently appeared at auction in Hong Kong in 2004, which of course is also the first and so far only time a yellow gold 5021 went under the hammer, 22 years ago. A timespan which solidifies into practical perspective the amount of patience collectors looking for one of these elusive watches should have to arm themselves with, were they to miss the present occasion.