So you send me the wrong color item and I use it for many months and only after seeing my sister got a different color which is actually the color I wanted, you’d not send me the right color?

It depends on what the business will get from the employee over the next 4 months. And will the customers they service remain? Would they also remain if they were fitted immediately without a replacement? There’s lots of factors to consider.

What will your net gain be from this employee giving you 4 months notice? If it works out that you will be profiting from this even while paying for the training then it makes sense. If you are going to lose money over this then I’d suggest canceling the training with the full expectation that oil get 2 weeks notice or less if they just quit.

What you need to do though is have this in a contract for the future. If someone leaves within x amount of time from taking company paid training, they owe the cost of training back to the company.