I have spent the last three years researching this kind of stuff and all the hard evidence is that serial numbering started in 1972.
In addition to serial numbers, I am also researching the old Paiste lines from the 50s and 60s. And let me tell, I have spoken with people at Paiste many times and they readily admit to not having the best grasp on their history... that many records have gotten lost over the years. That they are just doing the best they can with questions about the old days.
There are ways to prove that the Swiss cymbals with 1xxxxx serials are from 1981 not 1971 (and the 0xxxxx cymbals are from 1980 not 1970). These ways include the ink stamping on the top of the cymbals and with Formula 602s the color of the size ink under bell is the biggest indicator.
Up until 1973 the diameter size ink under the bell of all 602 cymbals (except SE hats) was red. In 1973, they went to black ink under the bell. Now, find some 602s with 0xxxxx or 1xxxxx serials, after that look at the color of the ink under the bell, it will always be black proving the cymbal is from 1980/1 not 1970/1. A second indicator to use is the two-line "Paiste Formula 602" stamp above the bell on top side of the cymbal - this ink stamp was not introduced until sometime in 1972 either right before or along with the serial numbers.
This also applies to 2002s. An original 2002 from 1971 (and early 1972) should just have a basic black ink "Paiste" ink stamp above the bell. And when you do find these rare 2002s they do not have serial numbers. Like the 602, the two-line stamp came later. The 0 and 1xxxxx 2002s you see out there all have the common two-line stamp (unless it's been cleaned/faded off) again evidence these cymbals are from 1980/1 not 1970/1. If Paiste was right about serials starting in 1970 there would be no preserial 2002s as the line came out in late 1971.
Also with 2002s another way to test and prove the 1972 start date for serials, is using certain sizes or models: the Black Label 17, 19 and 21" size 2002s did not come out until late 1978 / early 1979 - you will find examples of them with 0 or 1xxxxx serials which means 1980/1 not 1970/1 because the cymbals were not released yet so it is impossible for the "0" or "1" to refer to 1970/1. Same goes for the Heavy 2002s, the Heavy Hats and 20" Heavy Ride did not come out until 1975 but you see them with 1xxxxx - again this proves the 1 = 1981 not 1971.
Most of the confusion regarding the serial numbers on Black Label Paistes stems from three things, imo.
1) Paiste providing customers with an erroneous date - they are using 1970 as a generalization when they should be saying early 70s if they can't definitively say 1972. You to have to keep in mind the people working at Paiste Customer Service now are younger people in their 20s and 30s - they were not around back then and don't know all the ins and outs of how the serial system works properly.
As an aside here... I know a drummer who knows Erik Paiste personally and Erik has told him that we are right about this, that serials started in 1972 first etched under the bell with month/year and then on top of the cymbals (for whatever that's worth)
2) The long-held, mistaken belief that the switch to the Color Logos happened across the board in 1980 - It did not - this happens in the early part of 1981. Yes, the RUDE series had the white logo in 1980 - the other, existing lines got switched over in 1981 (probably by late spring 1981). This has been proven many times by looking at the lowest serials on the 80s era Color Logo cymbals and by Paiste catalog and advertising material. The reason you see so many Black Label 2002s and 602s with 1xxxxx serials out there is because they were made for the first few months of 1981 and around this time is when Paiste starting becoming way more popular in USA so they were now making a lot more cymbals as compared to earlier in the 70s.
*** Going back to make a point about Paiste Customer Service here, the people working there now look at a Black Label cymbal with a 0 or 1 serial number and will tell you 1970 or 71 because they associate the BL cymbals with the 1970s and the Color Logos with the 1980s. That is why drummers who ask keep getting the wrong answer to this question, imo.
3) People not understanding how the serial numbers on the German-made Paistes work and are assuming the very old looking cymbals they see are from 1971. They are not... the German serial system is different. The Black Labels (and this goes for all Black Label lines made in Germany during the 70s: Stambul, Dixie, 404, 505, Super etc) will all start with a 1 or 2. They are numbered consecutively not first digit equals year of production. The second digit on a German "1" cymbal tells the story. The higher the second digit the deeper in the 70s the cymbal was made. i.e. a 14xxxx German BL is from the mid-70s while a 19xxxx is from the late 70s ('78 or '79). The Black Label Germans with a 2xxxxx were made ranging from probably late 1979 to early 1981. Not 1982, by 1982 all cymbals had the color logos.