
Could be, especially if you know your bitch well. I tended to see mine 'come out of season' pretty soon after being mated, although one came back into a coloured discharge after two good matings, which lasted to the very end of that season. I thought she'd never taken. However after an uneventful pregnancy, she produced 9 super puppies.
I tended to see some thickening of the flanks, but not until about week 4.
Each is different and my best advice, as I see no point in scanning other than a need to know with an unplanned mating, is to wait and plan for a litter. You'll see puppies moving around by about week 7 in any case. For me, scans only confirm or not, a pregnancy at the point of scanning. There's no guarantee a positive scan will mean a positive outcome and most often, scans aren't accurate. If nothing happens after a couple of days beyond her due date, then I go for x-ray and treatment depending on what x-ray says. eg. a shot and if that doesn't get things moving, C.Section.
ps The length of a tie doesn't matter. Breeders prefer to see a tie but one of my boys never tied his bitches but his strike rate was 99.9%