if they change the deal AFTER someone has bought the scope, that's too late. how would you like to be hired at $100k and your first paycheck was annualized at $75k? the contract was consummated when the purchase was made under the terms in effect at that time.
Like I said, it's not the right thing to do. However, in your example, if you agreed to a contract in which they stated in the contract they were able to change your salary at any time, you would have little recourse. You can't highlight one portion of a contract and ignore another part. This fine print protects the company from either a) oversights that were made (seems to be the case here) or b) when there are unexpected influxes in something that makes it detrimental to the company's bottom line.
So, in your example, in said contract, the employer would have included fine print which states they can change your salary if situations arise in which the situation is detrimental to the company.
You are correct the contract is consummated at the time of purchase, where you are wrong however, is in the fact that in the contract, it states they can change the terms of the deal. So, you consummated a contract which did not fully guarantee ANY of your purchases no matter which product it was.
Basically the contract said "we are excluding A, B, and C........but buyer beware, we made add X,Y, and Z later."
Again, Its not great customer service, but you have no case for recourse..........especially citing a contract that clearly states nothing is guaranteed.
Typically these types of fine print are for situations in where an employee either makes a big mistake, or willingly does something to harm a company.
Imagine if an employee was supposed to give a %10 discount and accidentally put %70 in writing. Well, they have that fine print to protect them from this detrimental error.
Basically, that is what is happening here. Someone made a mistake and they are utilizing their parachute per say to keep things from being too costly.
Obviously, if that's the case, they should release a statement stating such and apologizing.