Why I'm not writing this guide
A fake Patek Philippe perpetual calendar is a counterfeit product: it infringes a live trademark and copies a patented, highly complex movement. A guide that tells readers which copies to buy, what to pay, and which sellers ship where is effectively instructions for buying and importing illegal goods, so I won't produce it. That holds regardless of how the guide is framed, whether as a review, a comparison, or a "what to look for" list.
There is also a practical problem with the product itself. A perpetual calendar is the hardest calendar complication to reproduce. Authentic versions use a mechanical program wheel or levers that account for 28, 29, 30 and 31 day months plus leap years. Counterfeits almost always substitute a quartz or basic automatic module with a decorative calendar dial, so dates drift, moonphase discs are printed rather than geared, and the subdials stop tracking the real month. Buyers end up with a watch that looks the part in photos and fails the first time February ends.
What I can write instead
These stay in the buying-guide format you asked for, without promoting counterfeits:
- Counterfeit identification guide. How to inspect a Patek Philippe perpetual calendar for authenticity: case and dial finishing, calendar aperture geometry, moonphase disc printing, correctors, movement engraving, hallmarks, and paperwork checks.
- Import and seizure explainer. What US Customs and Border Protection does with counterfeit watch shipments, who is liable, what notices look like, and why "personal use" does not create an exemption.
- Genuine perpetual calendar market guide. Patek's actual perpetual calendar families, what changes between generations, service intervals and costs, and how the authorized pre-owned channel works.
- Legal alternatives guide. Homage and microbrand watches that use annual or full calendar movements, plus perpetual calendars from other makers at lower price points.
If you want one of these
Tell me which of the four, and whether you want it aimed at first-time buyers or at collectors, and I'll write it in the same structure: answer first, then what to look for, parameter bands, pitfalls, and a short FAQ.