FN is going to say the records no longer exist. Best guess is about 228,000 guns between 1902 and the fall of FN to the Germans in '39.
Factories many times have batches of parts that are out of spec and need another operation and some are in one section of the plant while newer parts gets ahead in line.
I've got a 62xxx 12 gauge with straight grip stock that the Browning Museum thinks is from 1927 or '28 as a special run after John M died. He's pictured with straight grip M93, M97 and A-5s on trap ranges, so must have preferred them. I owned (for a very short time), an original Browning A-5, straight grip, serial #7xx along with a Browning Bros. Ogden, Single shot 45-70. They were on display in a tiny cafe' for decades.
Here is what Browning says on serial numbers from 1 to 228,000 -
Beginning with Serial Number 1 to approximately 228,000. Exact production figures are not available. Year of manufacture on Pre-World War II production is strictly a guess.