in small stages vs bit-by-bit

in small stages and bit-by-bit both are adjectives.

Word	Noun	Adjective	Verb	Adverb
in small stages	No	Yes	No	No
bit-by-bit	No	Yes	No	No

As adjectives, in small stages and bit-by-bit are synonyms defined as:

Other synonyms of in small stages include piecemeal, step-by-step, stepwise.

in small stages (adjective)	bit-by-bit (adjective)
one thing at a time	one thing at a time