I'm not trying to be a jerk here, but you simply do not understand what you are reading. Why then would it make a difference if the seniority date was before August 1st versus seniority date after August 1st? Both seniority date before and after August 1st still get the progression, so tell me what the difference or the significance of having seniority before or after August 1st if what you are saying is true? You have to understand sentence structure and subject matter. Article 41 is talking about full-time employees with a seniority date of August 1st. Section 2 subject matter is talking about employees entering a full-time position with seniority date after August 1st. Read section 2 and tell me if they are talking about full-time employees with a seniority date before August 1st...
I don't know all the precedent, or have all the answers. Clearly the language is confusing, and all unclear language should be challenged. I'm not saying you shouldn't grieve it, I'm mostly playing devil's advocate.
I will try, however, to answer your question the best I can based on the language. The difference between people in progression as of the beginning of the contract (prior to August 1st) and those who start progression on or after August 1st is which progression they are in. Prior to August 1st you were in the progression as outlined in the old contract.
The language in section 1 about full time employees already in progression receiving the above contractual increases is the only thing that establishes that you got an increase as of August 1st, without it you would have to wait until your next anniversary date to bump up to the next progression rate.
You get the contractual increase as of the start of the new contract, but the next line says you will be paid no less than what you are entitled to according to section 2 below. The language in 2c was chaged specifically to state that employees in progression under the last agreement will be slotted into the new progression. Thus your increase brings you up to the rate you are entitled to under the new progression.
This language had to be changed from the last contract because, in the last contract, progression went from 3 to 4 years. The last contract had language protecting people in the 3 year progression from being bumped up to a 4 year progression. Since the progression schedule has not changed, just the rates, that language had to be changed.
Once again, the contract does not specifically state a date that the increases must take place, simply that the increases must take place each year. While in progression, the only time August 1st means anything is this year. After that, as long as you get an annual increase, and it is no less than what you are entitled to under section 2 and is at least as much as outlined in section 1, there is no contractual breech.