Can't agree more. With the advance in technology, everything can be forged. College graduation certificates, passports, watch case, serial numbers, gold seals inside watch cases (I have seen this in flesh - a 18k Cartier white gold Baignoire with bracelet, I was told only the movement and the box are original, the case, the bracelet, the zeals and number? No) ..., you name it.
That said, It's not uncommon to see "open" Patek certificates going around in the secondary market, especially for those references produced before the late 90s. When I bought my first Patek back in 1997, the AD suggested that they leave the paper not dated, and in case there's any problem with the watch, they could extend the warranty period for me. Don't really know this can be encouraged. Not quite moral, but it's a "service" to their customers. So, the Certificate of Origin in my vault is still with any date, but it does have the AD's company chop.
However, I think we should all be careful when buying newer models. As all the community members here know, Patek has been very careful in controlling flipping of their watches (through controlling those loyal ADs), starting with the period when 3712 was launched, so there should not be, in theory, many open papers for recent models in circulation.
There are numerous watch shows and jewel shows in Hong Kong, where I reside. So, I buy only the seller, not the watch, and I believe I won't have the luck to get any deals that are too good to be true. I never won a lottery anyway.
Francis