Wrong Transmission Fluid 100,000 Miles ago

[Qwoo8]

About 5-6 years ago when our 2007 Toyota Yaris was at about 100k to 120k miles I changed the Transmission fluid. I went to the local Toyota Dealership and they gave me Toyota Automatic Type IV Transmission Fluid and I did a drain and fill.

We later bought a 2006 Toyota Matrix with 60K miles since my wife converted me to these types of Toyota's (Same Oil, same filter, awesome mileage and engines). Now the Matrix is at about 115k miles and I changed the Transmission Fluid with the Type IV Fluid as stated in the manual. I bought 6 quarts + I had about a 1/2 a quart from the change years ago. I then pulled open my manual and see that the matrix takes the Type WS and that they aren't compatible. The Yaris is at 220K miles and is still running great (Did do water pump, thermostat, coolant a few months ago). I just ordered type WS I don't notice any shifting issues but the fluid is darker and looks ready to change.

Im really annoyed that the dealership service/parts employee gave me the wrong fluid years ago but I haven't had a catistrophic failure. Im thinking change the fluid and then maybe do it again to keep it fresher. I guess I could have a flush but it does have more miles. Would it be terrible to drop the pan and change the strainer. I hear that they don't always fit properly.

What are your thoughts? I really like my Yaris and want it to go for long long miles I hope this won't keep it from fulfilling its potential.