Crumpton (39) was shocked after winning the marathon in Invercargill on Sunday to find she had been listed as a masters runner.
Computer problems in the entry process meant Crumpton, training partner and women's silver medallist Gabrielle O'Rourke, and men's silver medallist Dale Warrender had been listed in the masters events by mistake.
Athletics New Zealand had moved to relegate Crumpton, O'Rourke and Warrender to masters events and declare third-placed Sarah Biss (Rotorua) the New Zealand women's champion.
But the national body backtracked yesterday, sport manager Brett Addison confirming Crumpton would be listed as the national senior champion.
The initial plan to consider Crumpton a masters runner had brought an angry response from Crumpton, O'Rourke and Wellington-based coach Kevin Ross.
The controversy started on Sunday night when Ross received an email from former New Zealand representative Chris Pilone that said Nikki Hamblin had been recognised as the half-marathon champion and Crumpton declared the winner of the masters title.
"This is very much short-changing Shireen," Pilone wrote.
"New Zealand open titles should go to the first athlete across the line."
The issue moved quickly on Tuesday.
Ross sent a strongly worded email to Athletics New Zealand high performance director Scott Newman.
"I feel strongly about this," Ross wrote.
"I did not conceive that Athletics New Zealand could be so stupid to devalue and insult the winners and relegate them to minor titles on the basis of age.
"I will be consulting my solicitor today to consider an approach in regard to age discrimination."
Crumpton was upset at the possibility of losing her national title.
"Neither Gabrielle or myself have ever entered masters events. We want to race as seniors and knew we could get medals."
Crumpton has won 12 New Zealand senior women's titles and wants her name recorded in the record books as the national champion.
Entries for the events were taken by the race organisers and not by Athletics New Zealand.
Addison said the situation arose for the half marathon in Auckland and full marathon in Invercargill because not enough information was collected from the athletes for the entry forms.
The championships were attached to annual local events.
In championship events organised by Athletics New Zealand, athletes must state whether they want to compete in senior or masters age groups.
"Unfortunately, for the half and full marathons, athletes were not given this opportunity and were placed into their age category based by their date of birth," Addison said.
Athletics New Zealand intends to change the process for next year.
