Historical B2B data spanning multiple years enables investment research, workforce planning, and AI model training in ways current snapshots cannot. The article profiles six providers - Coresignal (broad B2B coverage since 2016), Bright Data, Revelio Labs (workforce data from 2008), LinkUp (job postings back to 2007), PredictLeads, and TheirStack - and argues that quality markers like consistency, point-in-time accuracy, and entity matching matter more than raw record count.