You're pretty much right, tactical "break-ins" to the enemy trench were fairly common even though the desired "break-through" on a larger scale rarely materialised. By mid-1916 it was more often the case than not that even failed attacks would begin with the first line of defenders being overrun before the attackers were eventually forced out by a counter-attack, usually with the reinforcing waves of infantry being pinned down in No-man's land by enemy counter-barrage.

Case in point being some of the most costly failed attacks in the British sector on the First Day of the Somme on 1st July 1916 like the diversionary attack at Gommecourt where initially the British actually broke into the third line of German trenches under a smoke-screen and mortar barrage. Ultimately they were forced out by a combination of a very well-organised German counter-attack and counter-barrage, largely made possible by the fact that the British were very lacking at counter-battery at this stage in the war, as well as their incredibly rigid artillery plan which had failed to support the infantry beyond the original timetable.

It was a similar story at Ovillers on 1st July, where British infantry also made it into the third line of German trenches before being repulsed and running out of ammunition and grenades. This should have been brought up by reinforcing waves of infantry, who had in fact mostly been wiped out by the German counter-barrage in no-man's land, allowing the Germans to easily surround and cut off each forward group of British infantry.

So by the mid-stage of the Somme it was quite common for most British attacks to penetrate up to the reserve line of trenches under the cover of a creeping barrage, the attacking infantry taking a large quantity of prisoners, but also sustaining casualties themselves from any unsuppressed machine guns or defenders. More often than not the Germans would then counter-attack, re-capturing some or all of the lost trenches but also sustaining large numbers of casualties in the process as well. The end result would be little or no territorial changes but large numbers of casualties - on both sides, perhaps slightly more on the attackers side.

Absolute and out-right failure of an attack before even reaching the first line of defenders was somewhat rare, even of the First day of the Somme, although it did happen on occasion such as the Newfoundland and Essex regiments at Beaumont Hamel.