If I am processing elements in the current-group (), is the
preceding-sibling axis restricted to the current group? I want to test
the value on a preceding-sibling element, but want to restrict it to the
group I am processing. Any pointers would be appreciated. I am using
XSLT 3. Thank you very much.

current-group() is simply a sequence of items you grouped together, they
can be from different trees, they can be atomic items.

If you want to operate item-wise on the sequence like current-group()
use xsl:iterate or xsl:for-each or perhaps a higher-order function.

Perhaps show us an example of the input data, the grouping code you have
plus the code to process current-group(), then explain which node(s) you
are looking for.