Sentinel lymph node biopsy

Husband had biopsy of mole 2.48 Brea low thickness.  Came back and we were told Clarks level 3.  Surgeon did WLE margins clear and skin checks every 6 months for other moles.  No referral to oncologist.  No sentinel lymph node biopsy.  Said he got it all and we were done no need to worry about that mole again.  2 years later cancer in nearly all of both liver lobes and elsewhere.  Why didn't general surgeon mention thr option of snb or perform one.  Seems everywhere I read everyone with that thickness had snb.  He failed to stage the cancer and we found out pathology report from initial biopsy said malignant melanoma!!  Anyone else not have snb with that thickness?  This was in 2015.  Thank you for your experiences.  I need peace of mind that I didn't fail my husband because I was naive.