Greedy spectrum allocation algorithms assign the required number of slots to a connection request as long as there are enough contiguous slots available for it. Instead, a deadlock-avoidance algorithm only assigns slots if future connections can be fit in the spectrum void left after assigning the current connection. That is, a deadlock-avoidance algorithm avoids leaving available slots that cannot be used by a future connection. The mean time required to exhaust the spectrum of a deadlock-avoidance approach has been studied in the context of a single flexible-grid link under incremental traffic. However, such algorithm has not been studied under dynamic traffic, where the blocking ratio is relevant, neither considering routes longer than 1 hop. In this paper we evaluate the blocking performance of greedy and deadlock-avoidance algorithms under dynamic traffic, in routes from 1-hop to 3-hops. Simulation results show that - with respect to a greedy approach - there is no benefit from deadlock-avoidance algorithms in 1-hop routes. However, the deadlock-avoidance strategy achieves up 2 orders of magnitude lower blocking than the greedy algorithm when longer routes are considered. This result highlights the importance of using algorithms that prevent spectrum fragmentation for efficient resource utilization in dynamic flexible grid networks.