I am sorry not to respond at this time to your original question. I am responding here only to the use of information elements.
IEEE 802.11 "7.2.3 Management frames
The frame body consists of the fields followed by the information elements defined for each management frame subtype. All fields and information elements are mandatory unless stated otherwise and appear in the specified, relative order. STAs that encounter an element ID they do not recognize in the frame body of a received management frame ignore that element and continue to parse the remainder of the management frame body (if any) for additional information elements with recognizable element IDs. A STA receiving a vendor-specific IE that it does not support shall ignore the vendor-specific IE.
"The ERP Information element is present within Beacon frames generated by STAs using extended rate PHYs (ERPs) defined in Clause 19 and is optionally present in other cases.
"18.104.22.168 ERP Information element
The ERP Information element contains information on the presence of Clause 15 or Clause 18 stations in the BSS that are not capable of Clause 19 (ERP-OFDM) data rates. It also contains the requirement of the ERP Information element sender (AP in a BSS or STA in an IBSS) as to the use of protection mechanisms to optimize BSS performance and as to the use of long or short Barker preambles."
The contents of the ERP information element are of interest only to ERP stations for backward compatibility with DSSS and HR/DSSS stations. HR/DSSS stations have their own features for backward compatibility with DSSS stations. I think of no instance of older PHYs being retrofitted, either in the IEEE standard or by vendors, with features for forward compatibility with newer PHYs.
I hope this helps. Thanks. /criss