The original Pong® brand arcade machine used a BCD counter for each player along with an extra flip flop for tens. The machine would end the game at either 11 or 15 points (operator-selectable) but if that were bypassed it could count up to 19. The General Instruments chip used in the vast majority of electronic tennis machines would play up to 15 points. When the original machine was created, there was a common off-the-shelf chip to convert a 4-bit binary number 0-9 into a seven-segment pattern, but the segment patterns for inputs 1010-1111 weren't useful digits. There were no common chips that would display those values as a repeat of digits 0-9. Since the GI was a custom chip, however, there was no difficulty having a 4x8 ROM which could convert four-bit scores into segment patterns for the numbers 0-15 directly.
I would expect that many microprocessor-based versions of the game would have kept the score as two BCD digits, which would allow values up to 99. I am unaware of any having made any provision for scores beyond 99, and doubt that any would have been designed in a way that could do so without explicit provision.
BTW, in the original machine, the BCD-to-segment chip is used twice for each player to generate tens and ones digits, but when showing the tens position the bottom bit is forced high while the upper three bits are set to the inverted state of the tens bit. Since the BCD-to-segment chip doesn't activate any segments for an input value of 1111, the effect is that the tens digit is 1111 (blank) until a player scores ten points, and then 0001 after that.
