"further backed up" is a correct phrase that can be used in written English.
It is used to indicate additional or stronger evidence or support for something. For example, "His statement was further backed up by witness testimonies."
The network's efforts are further backed up by an internal sustainability website for sharing best practice, called Acts of Green.
And their accounts are further backed up by at least a dozen conversations with other Alawites who had fled from Aqrab.
This was further backed up by brain-imaging studies, which show how much the literal and metaphorical are closely linked in the brain.
It risks fostering a dependence on services, as warned against in the government's green paper Independence, Well-being and Choice [pdf] and further backed up by the Commissioning for Better Outcomes guide [pdf].
This was further backed up by the fact tickets to the Star Wars film were available from the 19 October, but Tarantino had only recently heard about the situation.
This was further backed up when the team compared 50-year averages of aerosol optical depths with the total sulphate in ice core over time (deposits of the salt increase after volcanic activity) and the total stratospheric level of air particles.
Demonstrators unhappy with leadership in one country or another were out in full throat, further backing up traffic, making the city even noisier.
Punch continues to wind down and the level of profit of these units compared with where Greene King thinks they should be further backs up the negative underlying trading story in the Punch managed houses division.
Update: During the Apple event, the company formally announced "over 10,000" Watch apps were now available, which further backs up the App Annie report.
The New York court said Facebook had raised "novel and important substantive issues," but declined to review the case further, backing up the lower court's denial of the challenge and calling it "nonappealable".
[Update 6/20/18 9 15am pacific: Instagram and YouTube celebrity Lele Pons posted that she's part of a special Instagram announcement today at 10am pacific. This further backs up our report that today's IGTV announcement is focused on creators.].
