I would not expect to see patent dates. If I am correctly seeing diagonal knurling on the brass adjustment wheel, this may be a Type 18 which was after many of the patents had expired.Bought my first plane, spent about $40 shipped to me from ebay, here are some pictures fresh out of the box. I guess the first thing I need to do is take it all the way apart, it looks like it has all the pieces. So far I do not see any patent dates on it, but I will keep looking.
Look for the Type Study in the upper right menu's then scroll down. Lots of pictures on this site for reference.
The plane looks to be in good condition. Not badly rusted, blade seems full length.
This should clean up well and be a very useful addition to your tools.