How can I use nested VLOOKUPs? [closed]

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I'm trying to give the lookup array for a VLOOKUP as a named array coming from another VLOOKUP.

Namely:

1) This works: VLOOKUP(C2, VendorExams, 3, 0)

I get as output CAT_exams which is the name of an array.

2) This works too: VLOOKUP(C2&D2, CAT_names, 4, 0)

I get as output the desired cell value from the CAT_names array.

3) Nesting them with (or without for that matter) INDIRECT, doesn't work: INDIRECT(VLOOKUP(C2&D2, VLOOKUP(C2, VendorExams, 3, 0), 4, 0))

I get an 504 error which indicates to me that the nested VLOOKUPs output is not understood.

Is this not-working-as-intended, a bug or am I doing something in a wrong way?

Using 4.2.3 if it has any relevance.