Yup...... my CS2220 was the same. When I picked up filters and fluid at the dealer for the 50hr service he told me I could reuse the fluid........but for a few extra bucks I was not going to try the 'vacuum hose method' to keep the fluid in .......and I was not going to strain/clean the old fluid after I drained it ......so the easiest was to just replace with new fluid.
The CS2220 only needs 10.1 litres so it is not a huge expense. I just finished the 200hr service and replaced filters and fluid again.......should be good now for awhile.
I believe the 50hr service mostly about getting fresh filters on as the factory ones will have build contaminants in them from the original assembly. The factory fluid is ok till the 200hr service, but is a PIA to try and hold back in the trans/hyd system or restrain/clean to reuse.
Your choice.......some axtra $ or time to ensure you keep the old fluid clean.
ps. be prepared to muscle the original filters off at the 50 hrS.......they are on tight and might even have been painted over during assembly. Rest assured they do come off, but they may have to be damaged in the process.