I have never seen a chart that dated EC Simmons era tang stamps? Sellens does give a couple of examples, but dates are a wide range. Below are a few different variations of EC Simmons Keen Kutter stamps that I have.
First are a couple examples of the standard tang stamp, in use from 1905 right through to late 1939.
Here is one that is missing the MO under St Louis
Below is the standard wedge and bar but with ears at the top of the wedge. This is commonly thought to denote a knife made by Camillus.
Below is an example of a stamp that has MADE/IN/USA in place of the standard ST/LOUIS. Sellens says it is believed that this stamp was used for a short period sometime in the 1920s. I have quite a few with this stamp.
Below are a couple of examples of what I think is a bit of a rare stamp. It has the ears at the top of the wedge and MADE/IN/USA. I have three knives with this stamp and have only seen one other example posted anywhere. I have no idea of a date range, other than sometime between 1905 and 1939, obviously.
Below is a stamp I have only seen once. It is on a pruner posted by Waynorth (upnorth on AAPK) over on BF. It has ST LOUIS/USA.