1. There is no maximum number of parts a drabble series/sequence can have.
2. Many people do post their drabble series/sequence in one work, either as separate chapters, or in one chapter with scene dividers. You are also welcome to post the parts as individual works in a series. (In the past, AO3 was buggy with anonymous series, making that option inadvisable, but the issue seems to have since been fixed.)
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1. There is no maximum number of parts a drabble series/sequence can have.
2. Many people do post their drabble series/sequence in one work, either as separate chapters, or in one chapter with scene dividers. You are also welcome to post the parts as individual works in a series. (In the past, AO3 was buggy with anonymous series, making that option inadvisable, but the issue seems to have since been fixed.)