Thank you very much Sam, now world seems to be a little bit easier, because from one side is solving problems and from the other finding the correct way of analyse the case.
I just want to add that that I needed to divide your stylesheet into two parts: one with the identity and second with the rest (started with <xsl:import /> of course), because I received an errors/warnings:
(using saxon and xalan as well)
XTRE0540: Ambiguous rule match for /term
Matches both "node()" on line 11 of file:/D:/xslt/n2_num.xsl
and "node()" on line 32 of file:/D:/xslt/n2_num.xsl
but the correct result was displayed.
After dividing everything works perfect. Real appreciate!