HI Prateek,
Completely agree with the questions you are asking.
The intent of the illustration I sent is to compare what a user of the software see as the GWP output of a product…suggesting that the results are not very comparable. EC3 is using A1-A3 only, and Tally uses all modules. For the Tally output, two EPDs are used: the CRSI one you referenced and one I cannot seem to find a link to (though the data is within Tally). Using the excel outputs from Tally, they average – based on the selections we made on rebar – to 1.48 MT CO2e/MT, simply by dividing the total GWP of the rebar by the mass of the rebar that Tally readily outputs. I am not sure of the algorithms within Tally that modify EPD data to produce this result because a majority of the input rebar data is based on the CSRI which is .979 MTCO2e/MT.
-Kjell