How many unique tag names can I have per order?

[Vismonkey]

I know that you can only have 250 tags per product, customer, etc... but my questions is how many unique tag names can you have?  For example, I would like to "tag" my orders with a PO number for easy search.  The problem is that if we are limited to only 250 unique names then I will run out after 250 orders or less.  Ideally, I would use a metafield to store the PO number on the order, but it looks like you can't search internally based on a order metafield.

thanks for your help.

[azamgill]

Hey @Vismonkey 
Instead of product tags, I think it's better to place PO number inside the product description. It also help your customer to refer your product. And if you type any word ie your product PO Number in the Shopify search then it will search the products with that number.

[Vismonkey]

Thanks for your suggestion, however this does not apply to my question. I
want to tag my orders with POs so that I can search them internally by the
PO number.