[theducks]

Originally Posted by paulfiera

It probably depends on your settings in...

# The algorithm used to assign a new book in an existing series a series number.
# New series numbers assigned using this tweak are always integer values, except
# if a constant non-integer is specified.
# Possible values are:
# next - First available integer larger than the largest existing number
# first_free - First available integer larger than 0
# next_free - First available integer larger than the smallest existing number
# last_free - First available integer smaller than the largest existing number
#             Return largest existing + 1 if no free number is found
# const - Assign the number 1 always
# a number - Assign that number always. The number is not in quotes. Note that
#            0.0 can be used here.
# Examples:
# series_index_auto_increment = 'next'
# series_index_auto_increment = 'next_free'
# series_index_auto_increment = 16.5
series_index_auto_increment = 'next'

Try with "next_free"

Otherwise, Kovid's your friend

More options than I had Pasted

Devs
Could we get a REV Date in the Beginning of the comments when a Tweak gets updated?

# V12/30/2010 The algorithm used to assign a new book in an existing series a series number.

I just flew by that one...Already Got it!