IMO, Do not use it. There is still enough visible that you can make out the date and mm. The acid will leave a tell tale sign and nearly always lowers the value of the coin (compared to one with a visible date in the same grade). The coin is probably worth less than $5 anyway so you aren't going to hurt yourself too much, but I would leave it. If you have a lot of experience with the stuff and can blend in the acid etched area and not leave a dark stain, then it might be worth trying on the MM, but I personally would leave it alone
You can read the date just fine. NIC-a-Date will stain the coin and lower it's value. I only use it on no dates. Surprisingly, I've found a few better dates. I know what they are but the value is higher than what I paid for a no date but lower than it should be as it's now damaged. With your pics upside down, all I have to do is stare at them for a minute or two and it appears the Indian and the Buffalo are recessed like the Gold Indians. Either that or I'm way too tired.
