There are complicated employment laws which need to be adhered to. As the companies are being merged together, the law requires the employees DoJ their original company to be respected as continuous service. Just like if BA merged into the Iberia pilot seniority list. They wouldn't expect to be shoved at the bottom like the BACC are planning here would they!?
When Bmed was merged with BMI the lists were merged together on DoJ with BALPA's direction.