I have never seen any such data sheets with Ilford or Foma papers I use.
Every box of Ilford paper I have ever used had a data sheet and......
fumbles around in cupboard for a packet of Foma paper...... wait a minute whilst I open it..... there is also a data sheet here!
GRADE.......1........2.......3........4.........5
DURST.....40Y....20Y....20M....60M....130M
MEOPTA...80Y....50Y....20M....60M....130M
Hope that lines up properly. EDIT: It didn't so I added some dots.
It doesn't really matter which scale you use but it would make sense to use the same one all the time. Or don't bother knowing which grade it is. Do a trial with no filtration (which the table above would indicate as being grade 2.5) and add magenta to increase contrast or add yellow to decrease.
You will need to do a test strip each time you change the filtration as the more you filter the light, the longer the exposure will need to be.
Steve.