All files before a certain date are missing on my Adobe Photoshop Cloud

For the future, You should always have a local copy of all files
If you don't have space on your computer drive use an external drive for files
A USB flash drive to keep in a safe place... here are 2, there are many more available
PNY brand https://www.amazon.com/PNY-512GB-Turbo-Attach%C3%A9-Flash/dp/B0BF5VHLBZ
SanDisk https://www.amazon.com/SanDisk-512GB-Ultra-Flash-Drive/dp/B083ZLJ5MG
Other flash drives are 1 or even 2 Terabytes
Formatting a flash drive https://www.usbmemorydirect.com/blog/flash-drive-format-types/

use a web browser to navigate to the following locations. at each location there are several folders/link to check.:

https://assets.adobe.com

https://lightroom.adobe.com

https://documentcloud.adobe.com

https://spark.adobe.com

if you delete anything from any of these locations, check for a deleted folder where your file(s) was (were) moved. if you want to clear space you must delete files in the deleted folder. the used storage shown at each of those four sites (when totaled), should match the space shown used by your cc files. more info, https://helpx.adobe.com/creative-cloud/kb/file-storage-quota.html?linkId=100000257885896