from one contract to an other keeping your seniority, not only on the seniority list but also on the paygrade
There is no seniority as such. You have a rank and that is about it! The only time seniority exists is within a base transfer list, in which case it is not improved by your length of service in the company: first on the transfer list, first offered transfer.
The only incremental pay is loyalty and only applies after a number of years and is only paid once per year as a bonus. There is no incremental pay scale. When you move from FO to SFO to Capt to Training Capt, you get a raise according to the promotion. That is your salary for that rank. The actual pay rates for each rank differ depending on local contracts and the applicable union agreements.
Hope that helps.