Manager and senior accounting technician Sharon Clarke was at the firm 42 years while Di Hawksworth leaves after 17 years in the administration team.
Her place in Scunthorpe's front office has been taken by Carla Mowforth, previously a civil servant for 34 years.
Sharon joined in 1978 as a filing clerk and made the tea before starting accounts work a year later and training with the Association of Accounting Technicians.
Sharon could “write a book” on the changes she has seen over her career.
“I think the most significant of those was the first computer being installed,” she said.
“The younger members of staff cannot believe that all accounts were done manually when I first started, from preparation to the final accounts being typed.
“The computer changed all of that.
“Initially we had only one which we shared with the secretary. We had to book a slot and make sure we were on and off in the allotted time.”
She was looking forward to retirement and has made limited plans.
“I will miss the interaction with the friends I've made over the years, and, I guess, to some degree, doing the interesting tax calculations, getting the grey matter working.
“I want to keep on top of the garden - it's been neglected over the last few years - and I want to concentrate on my dressmaking and crafting.
“But my main plan had been to travel and see some more of the world.”
Sharon was looking forward to having time the most.
Di was at NatWest Bank for 20 years before switching to Crown Accountancy Services in 1999.
It merged with Coleman & Co and then joined RNS in March 2004.
She said: “RNS has a great team of people so I will miss working with them, especially my brother Mike.”
COVID-19 has stopped her making plans but, when she can, Di hopes to travel around the world visiting places she has not been before.
On the list is Canada, Australia and New Zealand and another trip to Thailand is on the itinerary.
“I'm looking forward to spending more time with husband Steve who has been retired for three years.
“I will carry on making greetings cards for family and friends and selling some, donating the funds to Lindsey Lodge Hospice.
“I'll also continue with my passion for crochet, especially making small animals and blankets.
“This year, I started Tunisian crochet so I'm looking forward to carrying on with that.”
Senior partner John Heeney said: “I would like to thank Sharon and Di for their loyalty and dedication over the years.
“They will be missed, and we wish them long, happy and healthy retirements.”