If you were, for example, an Elf who rolled an 18 and put it in DEX, you had 19 DEX. There was, AFAIK, no actual rule against that in 1E AD&D. Quite a few groups had a house rule that no stat could be over 18 because they didn't have values for those stats until Deities and Demigods came out. Certainly the 1E players I knew insisted this was the case. Whereas 2E explicitly capped stats based on race, usually at 18. So the 1E players would try to drag in 1E races we didn't have explicit 2E stats for, and thus not explicit limits. A few 2E races had 19 or 20 caps too - for example Bakali Lizardmen had 19 STR and CON caps (and +1 STR/CON).