the dummy field name missing in the drop down list

i am using the 2.50 version of mp3tag.
i have a title like this.

49 parimalar kulir-inh100514448

i want to omit the last word from it. i tried tag-filename conversion.
format string-%title%-%dummy%
but it is not giving the result. why this is not working?

moreover i don't find the word dummy in the drop down list of field can i bring the word dummy into the list?

i even tried guess values. there also i don't find the dummy on the drop down list of field names. i had to type it and it worked like this
guessing pattern>%title%-%dummy%
and i got the desired result as
49 parimalar kulir

If you want to rename a filename (and not put it together from the tag information) you would have to use the converter filename-filename.
Input mask:
Output mask:

Also, %dummy% is sort of bin to put data you do not want. So %dummy% does not contain any useful data.
It is not included in the dropdown list as it has no contents. You have to "know" it - or read about it in the online help.