Update README.md

README.md

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 # Introduction
-This is the implementation of the BERT model using the LongNet structure (paper: https://arxiv.org/pdf/2307.02486.pdf). The model is pre-trained with 10-K/Q filings of US firms from 1994 to 2018.
+This is the implementation of the BERT model using the LongNet structure (paper: https://arxiv.org/pdf/2307.02486.pdf). 
+
+The model is pre-trained with 10-K/Q filings of US firms from 1994 to 2008. Filings from 2009 to 2013 are used for model validation, and filings from 2013 to 2018 are used for model testing.
 
 # Training code
 https://github.com/minhtriphan/LongFinBERT-base/tree/main