The old 231 was an epic journey between Newcastle and Hartlepool that stopped everywhere and took nigh on two hours to complete. There was a limited-stop express service that also operated between Newcastle and Hartlepool (X5), so I don’t think that this service was aimed at anyone who needed to commute between the two areas. But, as mentioned, the X5 was a limited-stop service that stopped only at ‘the timing points shown’ without any additional stops. So if you lived in a village/community that the X5 did not stop at; then you were stuck with the 231.
Both services operated a similar route between Houghton-le-Spring and Hartlepool operating via Peterlee and Blackhall Rocks. Before the routes merged so to speak, the X5 operated the exact same route as the current ‘Red Arrows’ X1 services does now via Washington, whilst the 231 operated via Chester-le-Street and Birtley. The 231 started/terminated at Worswick Street whilst the X5 operated from Eldon Square via Worswick Street although in later years both services went to Eldon Square once Worswick Street had closed down. Both services were operated jointly by United and Northern.