Looks like the current limit for the number of attributes for secondary indexes on a table is 100 (not 20).
"You can project a total of up to 100 attributes into all of a table’s local and global secondary indexes. This only applies to user-specified projected attributes."
Yep, AWS routinely lifts limits for many of its services. I thought I had updated that in all the slides but guess I missed one.
However, because they regularly update limits, you won’t see a question on the exam on the exact numbers for limits…otherwise the tests would need to be updated constantly too…and AWS doesn’t want to do that.