For single crystals can I give BET data in the publication if it is coming around 200. And why it shows zero value surface area but after detag ads or des it shows value, and which one I should ads or des detagging the other.
Surface area is usually calculated from adsorption isotherms. If you are using quantachrome softwares, probably detagging ads or des are hiding data from the calculating algorithm.
Before publishing your BET surface area, I advise reading at least the IUPAC report (2015), just the value of 200 is not enough for me to advise you, you need your r², the type of the isotherm to see if the BET can be applied, and C constant, the report discuss those details.