I am also not certain of this, however you should be paid in accordance with your level of contribution to the work you do.
The apprenticeship period is usually four years, if you have been fast tracked to the second year of college such that you are now only doing an apprenticeship of three years then your pay should be increasing faster to reflect this as you will be able to provide the level of service that would normally be provided by someone who is maybe half a year ahead of you in physical time.
If you are to be paid based on period of employment it would be expected that at the end of your apprenticeship you would then be paid a standard salary for the permanent position.
Would it be expected that you would complete your apprenticeship (in three years) and then do a another years work as a fully qualified electrician at the pay of a fourth year apprentice? Not really!
If you were to leave your current employer now and start with another employer would your salary then revert to first year apprentice as this is your period of employment?