@Craig - Here are some comparative differences between the two.
There is a distinct difference in the lids. Just below the handle, the Pat Pending (69-70) has a flat, saucer sized area. Getting a photograph showing that flat spot on the Pat Pending was challenging. It is easy to see in person but I had to find the exact lighting and angle for it to show up in a photo. Is this where the term "Flat top" comes from"?
It is not present on the 78 and is more uniform in its curvature.
Looking at the bowl vents, they appear to be the same spacing.
Putting a tape measure to them I found a slight 1/2" difference in the vent spacing. This photo also shows that both have a flat spot in the middle of the bowl that only the Pat Pending has on the lid.