Cleaning is a controversial topic here, while conservation isn't (sorry, being snarky). If a coin is actually dateless it would really have to be a key or semi-key to be worth anything. If the date is just obscured with crud or some environmental material, there are ways that won't damage the coin, but you have to be very careful. Soaking and rinsing are accepted with pure, non-corrosive solvents, but brushing and wiping can be detrimental. Post a picture and more specific comments can be made.
Assk coin talk first. With a picture. Got to say. Never ever clean your coins before you post a pic. Thesse members can smell a date before you clean it. Trust me.
I have about 5 right now that the dates can only be partially seen. I'll send pictures as soon as I have a day to work on it. Thanks, guys.