In general, it’s not a good idea to reuse letters. Professional letters differ from recommendation letters in that they frequently use more precise language than the former. Additionally, you’ll need letters of recommendation from specialists who may not be your coworkers or past employers.
Therefore, even if you already have letters of support from experts written expressly for earlier visa petitions, you ought to still acquire new letters for your petition. Nevertheless, you could use the recommendation letters if you are certain that they contain all the details you require for your EB-2 NIW petition.